The present invention relates to a detonator for a nonelectric detonation system for blasting charges, primarily intended for interval delay blasting, but also usable in the initiation of individual charges. The present invention also relates to a specially designed booster charge adapted to the detonator.
In delay interval blasting above ground, non-electric detonation systems are generally preferred, since otherwise extreme vigilance must be maintained against the risk of electric storms and the use of radio transmitters in the immediate vicinity. This latter means of communication may constitute a particular problem, since today's contracting and mining industries are making increasing use of communication by radio for work supervision. The use of electric drills and loading machines has also increased considerably, particularly in tunelling work.
PETN fuzes or other detonator fuzes may advantageously be used for a more or less instantaneous initiation of a plurality of blasting charges. It is also possible to initiate the different charges in a delay interval blasting operation by means of a detonating fuze, but in such cases special individually delayed detonators are required which transmit the detonation impulse from the detonating fuze to each respective major charge or booster. A number of different but closely related time delay fuzes of this type and booster charges adapted thereto are disclosed in U.S. Pat. Nos. 4,060,033 and 4,165,691, and also in laid-open EPO Application No. 0,164,941. According to the two U.S. patents, the booster charges are constructed in mutually reminiscent manners, with an insulated tunnel along their one longitudinal edge in which a PETN fuze may pass. Furthermore, the charges are provided with a bore or a groove close to their second longitudinal edge in which the detonation cap of the fuze with its associated delay assembly may be placed. Furthermore, the fuzes described in each respective patent specification are designed with communication means angled from each respective detonation cap and extending across the charges and up to the tunnel for the PETN fuze where they are provided with a pyro assembly. Thus, the intention is that the pyro assembly be initiated when the PETN fuze detonates. The fire from the pyro assembly is then led, through the intermediary of the communication means (which, according to U.S. Pat. No. 4,060,033, is to consist of a low-strength detonating fuze, and, according to U.S. Pat. No. 4,165,691, of an empty, angled plastic tube) further to the delay assembly of the blasting cap in order, to initiate the blasting after the pre-determined time delay cap and, in its turn, each respective booster charge.
Albeit the basic principles of these two charges with their associated detonators may be satisfactory, their detailed designs are nevertheless afflicted with a number of serious drawbacks. Thus, the detonators are designed as elongate, angled members which are sensitive to disruption and may be difficult to mount them in place if the blasting operation is to be carried out during the winter and the charge layer is obliged to work with gloves. Moreover, the insulated tunnels for the PETN fuze are disposed along one longitudinal edge of the booster charges, with the result that the PETN fuze cannot be used for lowering the charges down into narrow bores, which would otherwise have been the most practical solution. The reason for this is that with the lowering cable, for example in this case the PETN fuze, disposed along the one edge of the charge, the "jammed drawer" effect is almost unavoidable betwen the relatively heavy charges and the drill riflings on the side walls of a narrow bore hole.
The booster charge and detonator according to EPO Patent application No. 0,164,941 have more practicable construciton, but neither can these be considered as fully satisfactory from all aspects. Thus, the booster charge consists of an explosive charge encapsulated in a cylindrical casing and provided with a first centered axial through-passage and a second passage disposed parallel with at some distance from the first passage, the second passage being, however, not necessarily a through-passage. According to the EPO application, a low-strength denotating fuze is led through the first passage and a blasting cap with built-in delay assembly is disposed in the second passage. As a communication link between the detonating fuze and the blasting cap there is further provided, in a specially adapted space in one end of the booster charge, a device which in the specification of this application is designated as a coupling charge. The consists of an impact or shock-sensitive detonating explosive encapsulated in its own protective capsule. To hold together the blasting cap, which at its one end face the coupling charge is provided with a percussion cap, and the coupling charge, a separate coupling block is employed. The coupling block is further provided with a slit tubular anchorage member which is intended to be passed down into the first passage for fixedly retaining the interconnected unit consisting of the blasting cap and the coupling charge. In its turn, the anchorage device is provided with a central channel with room for accomodating the detonating fuze.
Thus, the apparatus disclosed in the EPO application offers a booster charge which is initiated by means of a centrally and axially placed detonating fuze through the intermediary of a specially designed and adapted detonator consisting of a separate coupling charge and a blasting cap united by means of a separate coupling block. The disadvantages inherent in this prior art apparatus are that it contains a plurality of different features which must be interconnected and, as a result will be most circumstantial to handle. At the same time, the separate provision of a coupling charge which is initiated by the detonating fuze and in its turn initiates the blasting cap entails the introduction of an extra detonation signal transfer stage which in itself involves increased risk of malfunction. In this context, it cannot be over-emphasized that booster charges of this type are normally employed for the initiation of such low energy explosives as are used in interval or deck blasting in open cast mining and quarrying and in contracting work in which every salvo contains immense amounts of explosives, for which reason any malfunction of the detonation system is wholly unacceptable. The major advantage offered by the detonation system according to the EPO application is probably that the component parts and details are--as is also pointed out in the specification itself--extremely well suited for mass production in modern automatic machines. In all probability, the coupling charge also requires extremely careful handling.